1. Technical Field
The disclosure relates generally to metal gate electrode fabrication, and more particularly, to forming an in-situ silicon (Si) cap for a metal gate electrode.
2. Background Art
In the integrated circuit (IC) fabrication industry, metal gate electrodes are increasingly being used as a replacement for doped polysilicon (poly-Si) gate electrodes for a number of reasons. A metal, for example, Titanium Nitride (TiNx), is deposited by physical vapor deposition (PVD) to form a metal gate electrode. A Si layer is then deposited over the metal layer. However, as deposited, the metal, i.e., TiNx, is not very densely packed and absorbed oxygen and water in the environment can exit from the deposition chamber. During subsequent processing, the trapped oxygen containing species can cause a re-growth of interfacial oxide on the Si layer, causing extra Silicon Oxide (SiO) layers to be formed. As a result, the metal gate electrode becomes thicker than designed. The extra trapped oxygen and contaminants can also affect the properties of the metal gate hence formed.